As electronic devices operate at higher speeds at higher frequencies, electrolytic capacitors used in power supply lines of CPUs are required to have noise reduction performance and quick transient response over wide bandwidths from a low frequency to a high frequency of about 1 MHz to 1 GHz, and to have large capacitances and low impedance.
Roll type solid electrolytic capacitors that easily provide larger capacitance than capacitors including plural laminated electrode foils have been put in the market. Roll type solid electrolytic capacitors are made by winding a positive electrode foil and a negative electrode foil laminated with a separator in between. Such solid electrolytic capacitors have superior high-frequency characteristics in addition to long life time and temperature characteristics, and accordingly, are widely adopted in power supply circuits of personal computers.
FIG. 4 is a partially cutaway perspective view of a conventional electrolytic capacitor 501 described in Patent Documents 1 and 2. Positive electrode foil 101 made of aluminum foil has a surface roughened by etching. A dielectric oxide layer is formed by anodizing the surface. Negative electrode foil 102 is made of aluminum foil. Capacitor element 105 is formed by winding positive electrode foil 101 and negative electrode foil 102 with insulating separator 103 in between.
Solid electrolyte layer 104 is made of conductive polymer impregnated in separator 103. Positive electrode lead wire 106 and negative electrode lead wire 107 are joined to positive electrode foil 101 and positive electrode foil 102, respectively, and are drawn to outside. Case 108 accommodates capacitor element 105. Case 108 is made of aluminum and has a cylindrical shape having a bottom. Sealing member 109 made of resin vulcanized butyl rubber has holes 109A and 109B which positive electrode lead wire 106 and negative electrode lead wire 107 pass through, respectively, and seals an opening of case 108.
Upon a voltage being applied to, solid electrolytic capacitor 501 may cause a leakage current generating heat, hence shortening its life time.
Patent Document 1: JP10-340829A
Patent Document 2: JP2007-103499